Break down the bolt and make sure the extractor and spring are clean and moving freely. Could try replacing the extractor spring also.
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Sorry for the long delay between the OP and now. I have so little time these days it's difficult to answer, much less actually take apart something to look at the things you guys are asking. I appreciate the feedback and questions. Thanks for taking time to help. This is a brand new BCG and upper, just had a cursory wipe down before shooting.
So I pulled out the AR, cycled different rounds through the mag by hand, and it happens if I'm shooting or if I cycle the bolt with the charging handle.
The bolt definitely still has it's ejector pin in there, and is preloaded with some pretty heavy spring tension.
I took the extractor off, because it's pretty easy, has a small 5 coil spring and a single o-ring, looks pretty standard. Clean and decent. No noticeable issues with extractor lip itself. it looks pretty smooth.
@zackmars are you suggesting trying to run it without the o-ring and just the spring?
Edit: I decided to take the o-ring off and cycle it by hand just to see if it would work, and it did in fact eject the round. Is it a problem to run the gun without the viton o-ring? should I just order a new ejector spring/o-ring set to replace the factory one? I should also note that the ejection is really weak and I would be surprised it was reliable enough to not cause doublefeeds or jams.